This invention relates to a plasma processing apparatus or a plasma processing method for processing, using a plasma formed in a processing chamber in a vacuum vessel, a plurality of film layers arranged on the surface of a substrate-like sample such as a semiconductor wafer arranged in the processing chamber, or in particular, to a plasma processing method suitable for the surface treatment of a semiconductor substrate or the like using the plasma.
The recent fine patterning of semiconductor devices has come to require a higher dimensional accuracy, i.e. a higher CD (critical dimension) accuracy for the etching process to transfer a mask formed by lithography to an underlying film. In the mass production field, the problem is critical how to secure the CD reproducibility in addition to high CD controllability. Generally, the CD is changed in the etching process by the fact that the reaction products generated from the materials to be processed are deposited on an inner wall of the etching chamber, the fact that the internal members of the chamber are consumed due to a long-term use and the fact that the temperature of the internal members of the chamber is changed, which in turn changes the sticking probability of the radicals to the inner wall of the chamber, resulting in a change in the plasma state having an effect on the etching performance.
In micro transistors, the capacity of a gate insulating film is required to be increased to control the short channel effect, and this problem has conventionally been solved by reducing the thickness of a gate oxide film. A decreased thickness of the gate oxide film, however, increases leak current, and therefore, materials having high dielectric constants (high-k) have been introduced for the gate insulating film. The hafnium oxide film (HfO2) is an example of the high-k material replacing the oxide film. Due to the incompatibility as materials between the polysilicon (poly-Si) electrode and hafnium oxide (HfO2), however, the prior art requires a structure formed of a metal film having a proper work function. Among the various metal materials used for this purpose, TiN or La is a choice as described in Semiconductor International, Vol. 2008/1, pp. 20-27.
In the conventional plasma processing apparatus, cleaning operation is conducted using the plasma for each wafer or lot. For example, plasma containing fluorine (F), chlorine (Cl) or oxygen (O) is used mainly for the cleaning process to remove carbon (C), oxide film, poly-Si and the nitride film. On the other hand, the metal or the like (for example, Al), which is generated by the consumption of the inner wall materials of the etching chamber and may be deposited on the chamber interior, is difficult to remove by the cleaning using the plasma alone. A technique is now under study, therefore, by which seasoning or the like process is executed before etching the product wafer to maintain a constant internal atmosphere of the chamber.
The method described in JP-A-2004-031308 is known as such a conventional technique. According to the disclosure of this conventional technique, the seasoning process is executed to deposit a reaction product containing Si as a component on the inner wall surface of the processing chamber of the vacuum vessel before etching the silicon wafer in the processing chamber using the plasma formed in the particular processing chamber. In etching the polysilicon (poly-Si) film to form the gate of the semiconductor device, for example, a method is disclosed in which the silicon wafer is seasoned by forming a plasma using a HBr, Cl2 or O2 gas or a mixture gas thereof, or the wafer deposited with an Al film is etched with a plasma generated by a mixed gas of SF6 and Cl2 to form an AlF film on the surface of the quartz member in the processing chamber immediately after wet cleaning of the processing chamber.
Also, as described in J. Vac. Sci. Technol. B24, 2191 (2060), a metal material (for example, TiN), if etched, is attached to the inner wall of the chamber and often difficult to completely remove by the cleaning with the plasma using the gas system described above.